Normal levels on ALT blood tests range from 10 to 40 international units per liter, while scores between 10 and 34 international units per liter are normal for AST tests, states MedlinePlus. The tests measure the amount of specific enzymes, alanine transaminase and aspartate aminotransferase, in the body.
ALT is primarily found in the liver, so if this organ is damaged, ALT results are affected, explains MedlinePlus. Therefore, the test is used to check for a liver problem, such as cirrhosis, liver cancer, mononucleosis and hepatitis. AST is most common in the liver, heart and muscles, though this test is also done to identify and keep track of liver diseases.